Research on securitization – the process of politicization aiming to increase security – stresses how important it is for security authorities to gain public support for their representation of threats and security measures. However, there is little research on how people understand and respond to securitization and even less so via social media. Research on security and antiterrorism discourse has rather focused on policy documents and journalism. This article analyses attitudes on Twitter in the wake of the Norwegian terror alert in July 2014. Using discursive psychology it provides novel insights into securitization as an argumentative process that has entered social media. The study analyses all tweets with the hashtag #terrortrussel (Eng. #terrorthreat) from individual users and, in addition, the initial statements by the Norwegian authorities. The results demonstrate that Twitter users are creatively using social media in response to securitization, endorsing attitudes regarding a number of themes: (1) the authorities’ announcement and ways of representing the terror alert; (2) the diffusion of responsibility to lay people for monitoring suspicious events and actors; and (3) the issue of ethnicity and blame. The study contributes to two research streams: studies of securitization and studies of antiterrorism discourse in discourse analytical research.